1. Field of Invention
The present invention pertains to valves used in subsurface well completions, and particularly to valves in tubing strings that allow well fluids to freely enter the tubing string from below the valve, but can isolate the tubing string below the valve from pressure applied to the fluid in the tubing above the valve.
2. Related Art
Tubing used in a subsurface well, such as production tubing, is generally assembled at the well site using sectional lengths or “joints”. A first joint is lowered into the well bore until its upper end is at the well bore (or platform) surface. Each successive joint after the first is then joined to the joint just below it, conventionally using “box and pin” threaded connectors, and the assembled section of tubing string is lowered into the well bore by the length of the added joint. The process is repeated until a tubing string of desired length is assembled.
It is generally desirable to allow well bore fluids to enter the tubing as it is lowered into the well bore. This is easily achieved by having an open bottom on the first joint, or otherwise providing fluid communication between the well bore and the tubing interior, such as by providing ports. However, it is important to insure the assembled tubing string can hold pressure. To insure pressure integrity, an operator needs to occasionally test such integrity, as various joints are added, by applying pressure to the fluid in the tubing interior. However, the fluid communication path between the well bore and the tubing interior prevents such pressure from building unless the communication path is selectively blocked.
One attempted solution uses a first nipple that is placed above a packer as part of the tubing string. A first plug can be run on slick line, wireline, coiled tubing, or pipe and set inside the first nipple to block communication between the well bore and the tubing interior. That allows pressure-testing the tubing to full pressure without setting the hydraulic set packer. With that configuration, the packer setting intake pressure port is not exposed to the tubing pressure that occurs above the plug. After pressure-testing, the first plug is removed and the tubing string is further assembled.
That method requires an intervention to set and remove the plug each time an operator wishes to pressure-test the tubing string. In addition, to set the hydraulic set packer, a second nipple must be included in the tubing string below the packer. A second plug is run and set inside the second nipple below the packer, and pressure is applied in the tubing to set the packer. The plug is then removed. This requires further intervention which translates to expensive rig time, especially in an offshore environment. Also, each intervention increases the risk of getting stuck in the hole, and could create a hazardous situation.
In an alternative solution, a nipple and plug is run below the packer, and a tubing fill valve is run above the nipple/plug, but below the packer. The tubing is filled through the packer filling valve. The packer filling valve is closed, preferably using some intervention-less method such as pumping fluid from tubing to annulus at a certain rate to create a pressure differential from tubing to casing that can be used to close the tubing fill valve. Pressure can then be applied in the tubing to pressure test tubing integrity. The hydraulic packer setting port is exposed to the tubing pressure since the plug (in this case) is run below the packer. Hence, the tubing can not be tested to the desired full pressure without setting the packer. Packer setting pressure is normally lower then the desired tubing test pressure. Therefore, the tubing can be tested only to the lower packer setting pressure, and that is undesirable in most cases.
After the (lower) pressure test, the tubing fill valve must be reopened by some means to allow the tubing to fill as the tubing is assembled and lowered into the hole. This takes more rig time and there is a possibility of swabbing the packer's sealing element due to fluid flowing past the packer element at a high rate while the tubing fill valve is not reopened.
Thus, a need exists to selectively isolate the fluid communication between the tubing interior and the well bore whenever desired while running in the hole, while still allowing the well bore fluids free entry into the tubing interior when pressure integrity is not being tested. There also exists a need to allow pressure-testing of the tubing to a desired pressure that is generally higher then the packer setting pressure, without setting the packer during the pressure test.